1. Field of the Invention
The present invention relates to an automotive fuel hose used for the transportation of a fuel such as gasoline, alcohol-containing gasoline (gasohol), alcohol, hydrogen, light oil, dimethyl ether, liquefied petroleum gas (LPG) or compressed natural gas (CNG).
2. Description of the Art
To cope with more stringent regulations against vapor emission of automotive fuel gases in recent years, there has been a demand for low-permeability fuel hoses. As a consequence, there have been proposed various types of fuel hoses employing a polyester resin which is advantageous since it has a high barrier property against a gasohol. However, a polyester resin is disadvantageously poor in hydrolysis resistance. To solve this problem, it is proposed that an innermost layer of a polyamide resin or a fluororesin which have an excellent hydrolysis resistance is formed on the interior of the polyester resin hose to make the hose less permeable and more resistant to hydrolysis (see, for example, Japanese Unexamined Patent Publications No. HEI7-96564 (1995), No. 2000-71407 and No. HEI6-23930 (1994)).
However, a polyester resin is difficult to adhere to other types of materials such as a polyamide and a fluororesin. Therefore, the polyester resin layer and the polyamide resin layer (or the fluororesin layer) are typically laminated by providing a special adhesive layer therebetween. In some cases, a surface treatment such as a plasma treatment or a sputtering treatment is performed on-mating surfaces of the layers, correspondingly complicating the production process.
Further, a fuel hose is required to have flexibility (or impact resistance) at low temperatures such as about xe2x88x9240xc2x0 C.
In addition, with recent growing awareness of environmental issues, the fuel hose is required to be composed of halogen-free materials so as not to generate hazardous substances such as dioxins during combustion thereof.
In view of the foregoing, it is an object of the present invention to provide a fuel hose which satisfies low-permeability requirements in conformity with stringent regulations against vapor emission of fuel gases, and is halogen-free and further is excellent in hydrolysis resistance, inter-layer adhesiveness and low-temperature flexibility.
In accordance with the present invention to achieve the aforesaid object, there is provided a fuel hose, which comprises an innermost layer comprising a thermoplastic polyester elastomer having a flexural modulus of 400 to 2000 MPa, an intermediate layer comprising a polyester resin and provided around the inner layer, and an outermost layer comprising a thermoplastic polybutylene terephthalate elastomer and provided around the intermediate layer.
The inventors of the present invention conducted intensive studies, mainly on materials for respective layers of a fuel hose of a laminate structure, to solve the aforesaid problems. As a result, the inventors found that the innermost layer of the thermoplastic polyester elastomer, the intermediate layer of the polyester resin and the outermost layer of the thermoplastic polybutylene terephthalate elastomer, can be laminated with a sufficient inter-layer adhesive strength without the use of an adhesive because the fuel hose is entirely produced from the polyester materials. With this structure, the hard polyester resin layer (intermediate layer) is held between flexible elastomer layers (between the innermost layer having a predetermined flexural modulus and the outermost layer). Therefore, the fuel hose has excellent flexibility, and less permeability to an automotive fuel and the like. In addition, the poorer hydrolysis resistance of the polyester resin is compensated by the innermost and outermost elastomer layers. Since the outermost layer is composed of the thermoplastic polybutylene terephthalate elastomer according to the present invention, the fuel hose has excellent flexibility, even at low temperatures. Thus, the present invention has been attained.